Proper Sizing Is Extremely Important When It Comes To Your HVAC System – Bigger Is Not Better

September 7, 2017

Bigger Is Not Always Better

Determining the correct size of residential heating and cooling equipment is extremely important in achieving comfortable interior conditions. The size of cooling systems is particularly critical for optimal energy efficiency and comfort. When equipment is over sized, initial costs are higher, efficiency is reduced, energy costs increase and comfort may be compromised. The reason for this that your equipment will operate in short cycles.
Correctly sized equipment is especially important in humid climates, where short cycling of air conditioning equipment can lead to poor humidity control. Similar to an automobile in stop – and – go traffic, the overall efficiency of an air conditioner, furnace, or heat pump is reduced by excessive cycling. More starts and stops accelerate wear and tear on the equipment.
Over sized systems also use more fan power for the blower and often exhibit more duct leakage due to high operating duct pressure. Finally, over sized air conditioners and heat pumps greatly aggravate the summer utility peak demand on hot days.

Use the right contractor

Beware of casual sizing estimates based solely on an old school formula of “dividing the square footage of your home by a number to obtain tonnage”. The residential equipment sizing procedures recommended for use in the United States are found in Manual J, which is produced by the Air Conditioning Contractors Association of America (ACCA). Computer programs are available to simplify the load calculations specified by Manual J. Once the heating and cooling loads are known, Pleasant Air will then select compatible equipment for you.
Unfortunately, ACCA approved sizing methods are often not used and over sizing is very common. In one large-scale survey, nearly 40 percent of contractors indicated that they purposefully over-sized equipment, citing reason such as “to reduce call backs”, “to allow future expansion”, or “customers demanded it”.

Sizing and Efficiency Go Hand In Hand

Manual J procedures determine the design and heating and cooling loads based on the amount of wall, ceiling, window and floor area, their insulation value, and the building envelope and duct leakage. Building orientation, roof surface color and occupancy can also make a difference. The sizing calculations for new construction should take into account the various efficiency measures incorporated in the home. As a home’s efficiency is improved, the recommended size of the HVAC system should be reduced.
Pleasant Air Inc. has a team of individuals who are certified in all Manual J procedures and have years of experience in properly sizing the Heating and Cooling needs of your home.

How To Determine the right size for your home

Insist that documented sizing calculations be performed on your home using the ACCA Manual J procedure. ACCA methods have sufficient built-in safety factors to accommodate most air conditioning needs. Therefore, it is important to follow all instructions in Manual J using precise area measurements and other specific data.
Be aware that exaggerating temperatures for indoor heating and cooling set points can have large impacts on required equipment sizing. Generally, Manual J recommends 75 degrees for cooling and 70 degrees for heating.
Select a programmable thermostat so that your home can be conditioned before you arrive, thus avoiding the temptation to over-size equipment for rapid cool-downs or warm-ups. This will improve sizing-related performance and potentially save energy associated with more reliable thermostats.
Select variable speed air handlers to gain important advantages for both humid and dry climates. In humid climates, many variable speed systems “ramp up” blowers slowly, providing energy savings and improved dehumidification.
You may call us at 910-208-4518 or go to our contact page and click on the “Request a Free Estimate” button.